Methods and devices for laying pipelines are widely known. One method of laying a pipeline is the so-called J-lay method. Other methods are also known, such as S-lay.
Generally, the pipeline which is laid is suspended at a free end from a pipeline laying vessel during the laying thereof. New pipe sections are joined to the free end during the laying of the pipeline.
Generally, at a point at which the free end of the pipeline is suspended from the vessel, hereinafter referred to as the suspension point, large forces are transferred from the pipeline to the vessel. In the field of marine pipelaying, there is a gradual development that pipelines are laid in ever increasing water depths. This implies that longer and heavier pipelines are suspended from the vessel and thus, the force which is exerted on the pipeline support by the pipeline shows a gradual increase over time.
In one method of pipelaying, the forces are transferred from the pipeline to the vessel via a collar on the pipeline which engages a pipeline support on the vessel.
A problem which is encountered is that the forces may become too great for a collar of a known size. In some cases, it may be an option to increase the size of the bearing area of the collar. However, this is not always possible or preferable. A bigger diameter generally means an increase in cost. In the case collars are made from thick walled pipe, there may be fabrication limits to the outer diameter of the collar.
Also, for pipe-in-pipe systems of the sliding type, on certain locations collars may be required on the inner pipe. The outer diameter of a collar on an inner pipe may become too large to fit within the inner diameter of the outer pipe. In such a situation, an increase in the size of the collar would necessitate a larger outer diameter of the outer pipeline. This in turn substantially increases the cost of the total pipeline system.
Another problem encountered in the prior art is that the forces which are transferred from the pipeline to the pipeline support induce stress concentrations in the pipeline or in the pipeline support. Generally, the contact between the pipeline and the pipeline support occurs in a support surface. Depending on the situation, these local stress peaks may become too high and damage may occur in the pipeline or in the pipeline support.
U.S. Pat. No. 5,458,441 discloses an example of a traditional J-lay system. One of the embodiments shows each pipeline section containing two collars. A movable clamp 32 engages a bearing area on a first collar 12, a fixed clamp 34 engages a bearing area on a second collar 18. No load sharing between the two collars occurs during lowering of the pipeline or during adding a new pipe section. When loads in the pipeline increase, the bearing areas of the respective collars have to increase in order to carry the load. This will lead to an increased overall wall thickness and thus a larger protrusion of the collars from the pipeline wall. An increase of wall thickness generally leads to an increase of production cost and makes it more difficult to manufacture collars with the desired mechanical properties.
U.S. Pat. No. 6,273,643 discloses a similar system as U.S. Pat. No. 5,458,441 and has a similar disadvantages.
U.S. Pat. No. 6,729,803B1 discloses a system which is based on friction. Shoes 17 are provided having bearing surfaces 21, A number of different shoes 17 are provided in different planes 11, which are vertically spaced from one another, see FIG. 3. Some load sharing occurs between the planes 11, see column 8, lines 51-67. However, a disadvantage of U.S. Pat. No. 6,729,803 is that it is difficult to ensure a proper distribution of the forces between the levels 11. In practice, the actual distribution of the forces will be relatively unpredictable.